1. Field Of The Invention
This invention is related to wellheads, to the control of wellheads and, in one aspect, to a solar powered wellhead control system for oil and gas wells.
2. Description Of Related Art
The prior art discloses a variety of controls for wellheads. Typically these apparatuses include one or more valves which are operable either on site or remotely in response to alarm conditions.
FIG. 1 depicts a typical prior art wellhead control system for controlling an hydraulically operated down hole valve or surface controlled subsurface safety valve ("SC-SSV"); a hydraulic/pneumatic master valve or hydraulic wireline cutter safety valve; and a hydraulic or pneumatic wing valve with quick exhaust device. Prior art systems such as this can be used for (1) single-point protection for flowlines, using direct-controlled surface safety valves ("SSV"); (2) multi-point protection for flowing wells and flowlines, using a pneumatic-controlled system with direct-controlled, tubing safety valves; and (3) a multiwell, multi-point protection system, using a combination of hydraulic and pneumatic systems to control both surface safety valves and surface controlled subsurface safety valves.
The equipment may be installed on a wellhead tree to protect against potentially hazardous conditions and from abnormal pressure situations in flowlines while providing complete shutdown capabilities. The pressure in each well's flowline is monitored by a specific monitor pilot which is located externally or internally in a control panel. The control panel monitors each well individually, and should flowline pressure exceed predetermined limits the monitor pilot is designed to block and bleed pneumatic control line pressure to close a safety valve on that particular well. Should an emergency occur, such as fire or damage to a wellhead, the control panel is designed to completely shut in the installation. In case of fire, the control panel reacts to loss of control pressure at the fusible plug. The control panel is designed to block and bleed both pneumatic and hydraulic pressure closing all of the safety valves.
Prior art control panels are designed to provide and control the hydraulic pressure required to hold open normally-closed surface and subsurface safety valves. Valves are designed to close with any loss of pressure in either the pilot or hydraulic lines to the valves. Control Panels are provided to control one well or multi-well installations, collectively or individually.
Prior art single-well control systems or panels enable the monitoring and protection of a specific well without affecting the status of surrounding wells. Such control panels are a complete unit containing a reservoir, pressure control regulators, relief valves, gauges and pumps with manual override. Being a complete unit, the control panel only requires connection to a power supply, to the safety valve, monitor pilot control line and to a gas or air supply line.
Prior art multi-well control panels are designed for safety systems which require control for more than a single producing well installation. These multi-well control panels use a module concept, either removable or integral. Each individual well control module contains components and display gauges essential for basic control of a specific well.
Several single wellhead control systems use pneumatic controls to monitor well flowing conditions, and emergency shutdown controls to close the wellhead valves. The source or media to operate the pneumatic controls is usually nitrogen, compressed air, or gas directly from the well itself. Each has disadvantages. Bottled nitrogen is costly, suffers from leaks, causes nuisance shut-ins, and results in loss of revenues. Compressed air requires electrical power and machinery. Natural gas does not provide the needed capacity in most case and the gas may be poisonous sour gas.
There has long been a need for a safe wellhead and wellhead control system that is operable by other than pneumatic power. There has long been a need for a wellhead control system that is solar powered. There has long been a need for such systems which can be used at remote sites. There has long been a need for such systems which can be placed adjacent or very near a wellhead while meeting the requirements of stringent electrical codes. There has long been a need for methods for the safe and efficient operation of wellheads and of their associated valves which methods do not rely on power provided from remote sources and which methods take into account responses to emergency conditions.